Macromolecules 1996,28,5684-5685
5684
Soluble Polyimides with Polyalicyclic Structure. 4.' Colorless Polyimides from Bicyclo[2.2.1]heptane-2-end0,3-endo,S-exo,6-exo-tetracarboxylic2,3:6,6-Dianhydride
Scheme 1 0
0
0
Toshihiko Matsumoto and Toshikazu Kurosaki* Department of Industrial Chemistry, Faculty of Engineering, Tokyo Institute of Polytechnics, 1583 Ziyama, Atsugi, Kanagawa 243-02,Japan
0
0
1
2
0
Yield: '7490, mp: 90.4 g:
R
Received February 21, 1995 Revised Manuscript Received May 23, 1995
0
Introduction Wholly aromatic polyimides are an important class of materials exhibiting not only excellent high-temperature stability, which makes them suitable for continuous high-temperature use due to their practical insolubility in common organic solvents, but also mechanical and electrical properties. Most of these materials cannot be molded as polyimides but must first be prepared as a soluble precursor poly(amic acid) and then processed into final form by thermal or chemical means. Moreover, the aromatic polyimides have strong reddishyellow color in almost all cases, which is caused by the inter- and/or intramolecular charge-transfer (CT) complex f ~ r m a t i o n . ~These -~ facts considerably restrict their practical application. Therefore, much effort has been concentrated on synthesizing soluble and colorless polyimides without sacrificing their desired proper tie^.^-^^ We have already reported the synthesis and properties of soluble polyimides from bialicyclic or tetraalicyclic dianhydrides and aromatic diamines.15-17 Although the polyimides that have been prepared so far have been almost colorless to pale yellow, most recently we found that entirely colorless polyimides could be prepared from a bialicyclic dianhydride, bicyclo[2.2.1lheptane-2-endo,3endo,5-exo,6-exo-tetracarboxylic 2,3:5,6-dianhydrideand aromatic diamines in the presence of a tervalent phosphorus compound on the polymerization. The present report relates the syntheses and characterization of the soluble and colorless polyimides.
0
3
0
Yield: 52C, mp: 252.4'c
Table 1. Polymers from 3 and Aromatic Diaminesa
polymer
diamine
4a 4b 4c
DDE DDM 1,3-BAB
4d
BAPS
4e
BAPF
(dug)* 0.80 1.16 0.77 0.70 0.70
T5 ("C) in Nf
filmd
470 484 445 456 496
flexible flexible flexible flexible brittle
Polymerization: diamine, 2.0 mmol; 3,2.0mmol; NMP, 5 mL; room temperature; 2 days; additional 2 days aRer adding a mixture of triphenyl phosphite (0.5 mL) and pyridine (0.2 mL). Imidization: 80 "C, 2 h; 250 "C, 2 h. Precipitated poly(amic acid). Measured in N M P at 30 "C at a concentration of 0.5 g/&. Sample form, film; 5% weight loss temperature measured by TGA with a heating rate of 10 "C/min. Polyimide film.
polyimide. The remainder of the polymer solution was poured into methanol. The precipitated polymer was dried under reduced pressure at room temperature for 1 day. The soluble polyimides were also obtained as a solid from the precipitated polymers by heating at 250 "C for 2 h under reduced pressure. Five types of the aromatic diamines were used here: 4,4'-diaminodiphenyl ether (DDE), 4,4'-diaminodiphenylmethane(DDM), 1,3-bis(4-aminophenoxy)benzene (1,3-BAB), bis[4-(4aminophenoxy)phenyllsulfone (BAPS),and 9,9-bis(4aminopheny1)fluorene(BAPF). Results and Discussion The poly(amic acid)s as precipitated possessed inherBicyclo[2.2.llheptane-2-endo,3-endo,5-exo,6-exo-tetra- ent viscosities (rinh) in the range from 1.16 to 0.7 dug. These results along with the film quality and the 5% carboxylic 2,3:5,6-dianhydride (3)was prepared accordweight loss temperature ( 7 ' 5 ) of the corresponding polying to a procedure which was a modification of a imides are listed in Table 1. The polymer solutions, previously reported one.18 The synthetic route is ilwhich were cast on glass plates immediately after the lustrated in Scheme l together with melting points and yields. Bicyclo[2.2.l]hept-5-ene-2-endo,3-endo-dicarbox- polymerization, formed flexible and tough polyimide films on heating under vacuum, except for that prepared ylic anhydride (1)was treated with carbon monoxide in from 3 and BAPF (polymer 4e). Thus, the presence of methanol in the presence of a catalytic amount of 5 % TPP/Py in these polymerizations usually enhanced the Pd/C and a stoichiometric amount of CuCl2 to afford the tetramethyl 2-endo,3-endo,5-exo,6-exo-tetracarboxylate film formability in a series of our polyimide syntheses, compared with ones prepared without it. TPP/Py works (2). The tetracarboxylate was hydrolyzed with hydroas a condensingreagent for the amide-linkage formation chloric acid followed by dehydration with acetic anhybetween the terminal amino and the terminal dicardride to give the dianhydride 3. boxylic acid groups of the polymer. The latter would Polymerizations of 3 with various aromatic diamines be formed by reacting the dianhydride with a trace referred t o below were carried out in N-methyl-2pyrrolidone (NMP) at room temperature in a nitrogen amount of contaminating water in the polymerization stream for 2 days and then for an additional 2 days with medium. Consequently, this might make the molecular the addition of more of NMP and a mixture of triphenyl weight of the poly(amic acid) increase and contribute to the enhancement of the film formability. Elemental phosphite and pyridine (TPP/Py). The polymerization proceeded homogeneously to a viscous solution without analysis of the polyimide films and the precipitated polygelation in each case. An aliquot of the poly(amic acid) (amic acidls revealed that the phosphorus content was solution was cast on a glass plate using a doctor blade below 0.1% and that these polymers did not contain a and then heated under vacuum at 80 "C for 2 h and unit derived from triphenyl phosphite. Interestingly, the IR spectra of the precipitated polymers showed that 250 "C for 2 h to effect cyclization to the soluble 0024-9297/95/2228-5684$09.00/00 1995 American Chemical Society
Macromolecules, Vol. 28, No. 16, 1995
Notes 6686
Table 2. Solubility of Polyimide Films Prepared from 3 and Aromatic Diamines
solvent 4a concentrated HzS04 m-cresol ++ sulfolane N-methyl-2-pyrrolidone Nfl-dimethylformamide Nfl-dimethylacetamide 1,3-dimethyl-2-imidazolinone dimethyl sulfoxide -
++ ++ ++ ++ ++
4b
solubility" 4c 4d
++ ++ ++ ++ + + ++ + ++ - + ++ - + ++ - + +- + +-
4e
++ ++ ++ -
-
+-
++, soluble at room temperature; f, soluble on heating; -, insoluble even on heating. the poly(amic acid)s partly contained the imide moiety; that is, the absorptions at 1765-1775 and 1710-1720 cm-l due to the imide carbonyl appeared weakly in addition to those of the carboxylic and amide-carbonyl groups of poly(amic acid)s at ca. 3300 and 1550-1650 cm-l. The TPPPy system has been well-known as one of the condensing reagents for amide-linkage formation from carboxylic and amino group^;^^^^^ therefore, the use of the TPPPy reagent system in the condensation for imide synthesis would seem to accelerate imide formation over amide formation. The thermal properties of the polyimide films were estimated by 2'5's measured using thermogravimetric analysis that was carried out at a heating rate of 10 "Clmin in a nitrogen atmosphere. All of the polyimides exhibit good thermal stability with the T5's over ca. 450 "C, although the T5's measured in air were somewhat lower (20-30 "C) than those obtained in a nitrogen atmosphere. The solubility of the polyimide films was investigated qualitatively, and the results are summarized in Table 2. The transmission W-vis spectrum of about a 20;umthick polyimide film obtained from 3 and DDM was determined. The polyimide film showed a cutoff at around 280 nm and was entirely transparent and colorless, whereas those prepared without TPPPy when polymerized were slightly reddish-yellow. The transmittances were 85-95% in the range from 350 to 700 nm. The film can compete in transparency and colorlessness with poly(ethy1eneterephthalate) that is known to be a colorless polymer film. This optical transparency and colorlessness over a broad range was also attained for the polyimides from 3 and the other diamines. Their nature is considered to contribute to inhibition of intraandor intermolecular CT complex formation by incorporation of a polyalicyclic unit in the polymer chain. Furthermore, because it has been reported that tervalent phosphorus compounds such as TPP served as an antioxidizing agent or as a reductant for N-oxides and peroxide^,^^-^^ TPPPy is thought to inhibit trace amounts of readily oxidizable compounds which are contained in the reactants and the solvent from being oxidized to colored substances during the polymerization or heat imidization. The colorlessness of the polyimide films was maintained up to 300 "C even when heated in air and 400 "C in a Nz atmosphere. It may be possible to endow the polyimides constituted of polyalicyclic-aromatic structures with colorlessness by using triphenyl phosphite and pyridine as condensing reagents.
Experimental Section Materials. Bicyclo[2.2.1]hept-5-ene-2-endo,3-endo-dicarboxylic anhydride (11, carbon monoxide, 5% P d C , CuC12, and triphenyl phosphite were of commercial grade and were used as received. Solvents and the other reagents were purified as described in the previous p a p e r ~ . ~ ~ J ~
Measurements. IR spectra were measured using a Jasco VALOR-I11 Fourier transform spectrometer. UV-vis spectra were obtained on a Jasco Ubest-50 spectrometer. Melting points were measured using a Seiko Instruments SSC/5200 thermal analyzer. Inherent viscosities were measured in 0.5 g/dL NMP solutions of poly(amic acid)s at 30 "C using an Ostwald viscometer. Elemental analyses were performed at the Shonan Analysis Center Inc., using the molybdic acidyellow method. Thermogravimetric analyses were performed using a Seiko Instruments SSC/5200 thermal analyzer at a heating rate of 10 "C/min in a Nz atmosphere. Polymerization. I n a 30-mL three-necked flask were placed a diamine (2.00 mmol) and NMP (5 mL), and then 3 (0.472 g, 2.00 mmol) was added. The mixture was mechanically stirred for 2 days at room temperature under a nitrogen atmosphere. To the resultant solution were added NMP (5 mL) and a mixture of triphenyl phosphite (0.5 mL) and pyridine (0.2 mL), and then the mixture was stirred for 2 days. An aliquot of the solution was cast on a glass plate using a doctor blade, and the remainder was poured into methanol (300 mL). The precipitated polymer was filtered off and dried at room temperature for 1 day under reduced pressure. The polyimide film was prepared by heating the glass plate at 80 "C for 2 h under vacuum and then at 250 "C for 2 h.
Acknowledgment. The authors thank Miss Satoko Ikuma for her technical assistance. This work was partly supported by a research grant from the Iwatani Naoji Foundation. References and Notes (1) Part 3: Reference 17. (2) Hasegawa, M.; Mita, I.; Kochi, M.; Yokota, R. J.Polym. Sci., Part C: Polym. Lett. 1989, 27, 263. (3) Hasegawa, M.; Shindo, Y.; Sugimura, T.; Ohshima, S.; Horie, K.; Kochi, M.; Yokota, R.; Mita, I. J. Polym. Sci., Part B: Polym. Phys. 1993,31, 1617. (4) Tokita, Y.; Ino, Y.; Okamoto, A,; Hasegawa, M.; Shindo, Y.; Sugimura, T. Kobunshi Ronbunshu 1994,51 (41, 245. (5) Harris, F. W.; Feld, W. A,; Lanier, L. H. Polym. Prepr. (Am. Chem. SOC.,Diu. Polym. Chem.) 1976, 17 (21, 421. (6) Oishi, Y.; Ishida, M.; Kakimoto, M.-A.; Imai, Y. J. Polym. Sci., Part A: Polym. Chem. 1992, 30, 1027. (7) Wusk, M. J.; Jha, B.; King, M. Polym. Prepr. (Am. Chem. SOC.,Diu. Polym. Chem.) 1991,32 (31, 218. (8) Gungor, A.; Smith, C. D.; Wescott, J.; Srinivasan, S.; McGrath, J. E. Polym. Prepr. (Am. Chem. SOC.,Diu. Polym. Chem.) 1991, 32 (11, 172. (9) Falcigno, P. A,; Jasne, S.; King, M. J.Polym. Sci., Part A: Polym. Chem. 1992,30, 1433. (10) Kunimune, K.; Kobayashi, R.; Kawashima, M. Jpn. Kokai Tokkyo Koho 3-134125, 1991; 2-294220, 1990. (11) Rogers, F. E. U.S. Patent 3356648, 1964. (12) St. Clair, A. K.; St. Clair, T. L.; Shevket, K. I. Proc. Diu. Polym. Mater. Sci. Eng. 1984, 51, 62. (13) Matsuura, T.; Hasuda, Y.; Nishi, S.; Yamada, N. Macromolecules 1991,24, 5001. (14) Jin, Q.; Yamashita, T.; Horie, K.; Yokota, R.; Mita, I. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 2345. (15) Itamura, S.; Yamada, M.; Tamura, S.; Matsumoto, T.; Kurosaki, T. Macromolecules 1993,26, 3940. (16) Yamada, M.; Kusama, M.; Matsumoto, T.; Kurosaki, T. Macromolecules 1993,26,4961. (17) Kusama, M.; Matsumoto, T.; Kurosaki, T. Macromolecules 1994,27, 1117. (18) Yamada,.M.; Kusama, M.; Matsumoto, T.; Kurosaki, T. J. Org. Chem. 1992,57, 6075. (19) Yamazaki, N.; Higashi, F. J.Polym. Sci., Polym. Lett. Ed. 1974, 12, 185. (20) Yamazaki, N.; Higashi, F. J.Polym. Sci., Polym. Lett. Ed. 1974,12,2149. (21) Sago, S.; Tomari, Y.; Kobayashi, T. Jpn. Kokai Tokkyo Koho 6-166808, 1994. (22) Cadogan, J. I. G.; Machie, R. K. Chem. SOC.Rev. 1974, 3, 87. (23) Cadogan, J. I. G., Ed. Organophosphorus Reagents in Organic Synthesis; Academic Press: London, 1979.
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